With the scaling down of semiconductor devices such as dynamic random access memory (DRAM), new materials with high dielectric constant are required. Indeed, in order to store a sufficient charge in a capacitor with a smaller surface area, capacitors with higher permittivity are needed. Among high-k dielectrics, Group 4 based materials, such as HfO2 or ZrO2, are very promising since their dielectric constant is higher than SiO2 or Al2O3. However, their dielectric constant varies depending on their crystalline form (Thin Solid Films 486 (2005) 125-128).
Thick ZrO2 layers tend to have a unstable crystalline phase and to have higher leakage current (Applied Physics Reviews (2012) version 14-9-2012). To prevent these defects, a thin layer of Al2O3 has been introduced in between two layers of ZrO2, forming a so-called ZAZ capacitor, stabilizing the crystalline phase and reducing the leakage current (Applied Physics Letters 93, 033511 (2008); J. Vac. Sci. Techno. A 4 (6), 1986; Microelectronic Engineering 86 (2009) 1789-1795).
The cubic/tetragonal crystalline phase of the ZrO2 layer, which is the phase having the highest k-value, has also been stabilized by doping ZrO2 with a small amount of silicon or germanium (US2013/0208403A1 for silicon and Journal of Applied Physics, 2009, 106, 024107; Microelectronic Engineering, 2009, 86, 1626; Applied Physics Letters, 2011, 99, 121909 for germanium).
Group 4 alkylamide precursors containing cyclopentadienyl ligand have been developed, such as the one show below (Dussarrat et al., WO2007/141059; Niinisto et al., Journal of Materials Chemistry (2008), 18(43), 5243-5247). These precursors show a higher thermal stability in comparison to the tetrakis alkylamide precursors.
wherein R1=H, Me, or Et; R2&R3=C1-C4 alkyl group
Similar to these compounds, Group 4 precursors containing silylcyclopentadienyl ligand have been described in the literature as shown below:
wherein R=Cl, NMe2, OSiMe3, CH2SiMe3, C6H5 and CH2Ph (Journal of Organometallic Chemistry, 2004, 689, 1503 for Ti methoxy compounds, JP2005/171291 to Tosoh for Ti alkylamino compounds, KR2008/0101040 to UP Chemical Co. Ltd. and Journal of Organometallic Chemistry, 1997, 547, 287 for Zr compounds).
A need remains for developing novel, liquid or low melting point (<50° C.), highly thermally stable, with low viscosity, zirconium precursor molecules suitable for vapor phase thin film deposition with controlled thickness and composition at high temperature.